212 research outputs found
Higher-order-in-spin interaction Hamiltonians for binary black holes from source terms of Kerr geometry in approximate ADM coordinates
The Kerr metric outside the ergosphere is transformed into ADM coordinates up
to the orders and , respectively in radial coordinate and
reduced angular momentum variable , starting from the Kerr solution in
quasi-isotropic as well as harmonic coordinates. The distributional source
terms for the approximate solution are calculated. To leading order in linear
momenta, higher-order-in-spin interaction Hamiltonians for black-hole binaries
are derived.Comment: REVTeX4, 20 pages, typos corrected in Eq. (124) and (130
LMC Self-lensing from a new perspective
We present a new analysis on the issue of the location of the observed
microlensing events in direction of the Large Magellanic Cloud (LMC). This is
carried out starting from a recently drawn coherent picture of the geometrical
structure and dynamics of the LMC disk and by considering different
configurations for the LMC bar. In this framework it clearly emerges that the
spatial distribution of the events observed so far shows a near--far asymmetry.
This turns out to be compatible with the optical depth calculated for the LMC
halo objects. In this perspective, our main conclusion, supported by a
statistical analysis on the outcome of an evaluation of the microlensing rate,
is that self lensing can not account for all the observed events. Finally we
propose a general inequality to calculate quickly an upper limit to the optical
depth along a line of view through the LMC center.Comment: revised version (minor changes) Accepted for publication in A&
Partial suppression of the radial orbit instability in stellar systems
It is well known that the simple criterion proposed originally by Polyachenko
and Shukhman (1981) for the onset of the radial orbit instability, although
being generally a useful tool, faces significant exceptions both on the side of
mildly anisotropic systems (with some that can be proved to be unstable) and on
the side of strongly anisotropic models (with some that can be shown to be
stable). In this paper we address two issues: Are there processes of
collisionless collapse that can lead to equilibria of the exceptional type?
What is the intrinsic structural property that is responsible for the sometimes
noted exceptional stability behavior? To clarify these issues, we have
performed a series of simulations of collisionless collapse that start from
homogeneous, highly symmetrized, cold initial conditions and, because of such
special conditions, are characterized by very little mixing. For these runs,
the end-states can be associated with large values of the global pressure
anisotropy parameter up to 2K_r/K_T \approx 2.75. The highly anisotropic
equilibrium states thus constructed show no significant traces of radial
anisotropy in their central region, with a very sharp transition to a radially
anisotropic envelope occurring well inside the half-mass radius (around 0.2
r_M). To check whether the existence of such almost perfectly isotropic
"nucleus" might be responsible for the apparent suppression of the radial orbit
instability, we could not resort to equilibrium models with the above
characteristics and with analytically available distribution function; instead,
we studied and confirmed the stability of configurations with those
characteristics by initializing N-body approximate equilibria (with given
density and pressure anisotropy profiles) with the help of the Jeans equations.Comment: 26 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Effective Theory of a Dynamically Broken Electroweak Standard Model at NLO
We consider the Standard Model as an effective theory at the weak scale
of a generic new strong interaction that dynamically breaks electroweak
symmetry at the energy scale (few) TeV. Assuming only the
minimal field content with the Standard Model fermions and gauge bosons, but
without a light Higgs particle, we construct the complete Lagrangian through
next-to-leading order, that is, including terms of order . The
systematics behind this expansion is clarified. Although similar to chiral
perturbation theory, it is not governed by the dimension of operators alone,
but depends in an essential way on the loop expansion. Power-counting formulas
are derived that indicate the classes of operators required at the
next-to-leading order. The complete set of operators at leading and
next-to-leading order is then listed, based on the restrictions implied by the
Standard-Model gauge symmetries. We recover the well-known operators discussed
in the literature in connection with the electroweak chiral Lagrangian and in
similar contexts, but we collect a complete and systematic list of all terms
through order . This includes some operators not discussed in
explicit terms before. We also show that a few of the previously considered
operators can be eliminated via the equations of motion. As another important
result we confirm the known list of dimension-6 operators in the Standard Model
with an elementary Higgs doublet, essentially as a special case of our
scenario.Comment: 35 pages, 1 figure; references adde
Astrometric and Timing Effects of Gravitational Waves from Localized Sources
A consistent approach for an exhaustive solution of the problem of
propagation of light rays in the field of gravitational waves emitted by a
localized source of gravitational radiation is developed in the first
post-Minkowskian and quadrupole approximation of General Relativity. We
demonstrate that the equations of light propagation in the retarded
gravitational field of an arbitrary localized source emitting quadrupolar
gravitational waves can be integrated exactly. The influence of the
gravitational field on the light propagation is examined not only in the wave
zone but also in cases when light passes through the intermediate and near
zones of the source. Explicit analytic expressions for light deflection and
integrated time delay (Shapiro effect) are obtained accounting for all possible
retardation effects and arbitrary relative locations of the source of
gravitational waves, that of light rays, and the observer. It is shown that the
ADM and harmonic gauge conditions can both be satisfied simultaneously outside
the source of gravitational waves. Their use drastically simplifies the
integration of light propagation equations and those for the motion of light
source and observer in the field of the source of gravitational waves, leading
to the unique interpretation of observable effects. The two limiting cases of
small and large values of impact parameter are elaborated in more detail.
Explicit expressions for Shapiro effect and deflection angle are obtained in
terms of the transverse-traceless part of the space-space components of the
metric tensor. We also discuss the relevance of the developed formalism for
interpretation of radio interferometric and timing observations, as well as for
data processing algorithms for future gravitational wave detectors.Comment: 43 pages, 4 Postscript figures, uses revtex.sty, accepted to Phys.
Rev. D, minor corrections in formulae regarding algebraic sign
Lorentz Covariant Theory of Light Propagation in Gravitational Fields of Arbitrary-Moving Bodies
The Lorentz covariant theory of propagation of light in the (weak)
gravitational fields of N-body systems consisting of arbitrarily moving
point-like bodies with constant masses is constructed. The theory is based on
the Lienard-Wiechert presentation of the metric tensor. A new approach for
integrating the equations of motion of light particles depending on the
retarded time argument is applied. In an approximation which is linear with
respect to the universal gravitational constant, G, the equations of light
propagation are integrated by quadratures and, moreover, an expression for the
tangent vector to the perturbed trajectory of light ray is found in terms of
instanteneous functions of the retarded time. General expressions for the
relativistic time delay, the angle of light deflection, and gravitational red
shift are derived. They generalize previously known results for the case of
static or uniformly moving bodies. The most important applications of the
theory are given. They include a discussion of the velocity dependent terms in
the gravitational lens equation, the Shapiro time delay in binary pulsars, and
a precise theoretical formulation of the general relativistic algorithm of data
processing of radio and optical astrometric measurements in the non-stationary
gravitational field of the solar system. Finally, proposals for future
theoretical work being important for astrophysical applications are formulated.Comment: 77 pages, 7 figures, list of references is updated, to be published
in Phys. Rev. D6
Fabry-Perot Absorption-Line Spectroscopy of NGC 7079: Kinematics and Bar Pattern Speed
We present Fabry-Perot absorption-line spectroscopy of the SB0 galaxy NGC
7079. This is the first use of Fabry-Perot techniques to measure the
two-dimensional stellar kinematics of an early-type disk galaxy. We scan the
infrared CaII line using the Rutgers Fabry-Perot (RFP), to obtain kinematic
data extending to -band surface brightness mag./arcsec^-2,
in a field of radius \sim 40\arcsec. The kinematic data, consisting of
line-of-sight velocities and velocity dispersions, are in good agreement with
data obtained along the major axis of the disk with standard slit spectroscopy.
Comparison of the exposure times required for slit and RFP spectroscopy to
reach the same limiting magnitude shows that the RFP is significantly more
efficient for mapping absorption-line galaxy kinematics. We use the velocity
data, together with our own deep broad-band photometry,to measure the bar
pattern speed, , of NGC 7079 with the model-independent
Tremaine-Weinberg (TW) method. We find km/s/arcsec;
this is the best-constrained pattern speed ever measured for a bar using the TW
method. From the rotation curve, corrected for asymmetric drift, we calculate
the co-rotation radius and find that the bar ends just inside this radius. The
two-dimensional character of these data allow us to show that the TW method is
sensitive to errors in the position angle (PA) of the disk. For example, a PA
error of 2\degrees can give errors in .Comment: Accepted to ApJ. 30 pages, 10 figures. Postscript version with high
resolution figures is available at:
http://www.exp-astro.phys.ethz.ch/debattista/personal/ms.p
Dynamics of Barred Galaxies
Some 30% of disc galaxies have a pronounced central bar feature in the disc
plane and many more have weaker features of a similar kind. Kinematic data
indicate that the bar constitutes a major non-axisymmetric component of the
mass distribution and that the bar pattern tumbles rapidly about the axis
normal to the disc plane. The observed motions are consistent with material
within the bar streaming along highly elongated orbits aligned with the
rotating major axis. A barred galaxy may also contain a spheroidal bulge at its
centre, spirals in the outer disc and, less commonly, other features such as a
ring or lens. Mild asymmetries in both the light and kinematics are quite
common. We review the main problems presented by these complicated dynamical
systems and summarize the effort so far made towards their solution,
emphasizing results which appear secure. (Truncated)Comment: This old review appeared in 1993. Plain tex with macro file. 82 pages
18 figures. A pdf version with figures at full resolution (3.24MB) is
available at http://www.physics.rutgers.edu/~sellwood/bar_review.pd
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